Place of articulation

Place of articulation

The active articulator usually moves in order to make the constriction. The passive articulator usually just sits there and gets approached. A sound's place of articulation is usually named by using the Latin ajective for the active articulator (ending with an "o") followed by the Latin adjective for the passive articulator. For example, a sound where the tongue tip (the "apex") approaches or touches the upper teeth is called an "apico-dental". Most of the common combinations of active and passive articulator have abbreviated names (usually leaving out the active half).
These are the abbreviated names for the places of articulation used in English:

bilabial

The articulators are the two lips. (We could say that the lower lip is the active articulator and the upper lip the passive articulator, though the upper lip usually moves too, at least a little.) English bilabial sounds include [p], [b], and [m].

labio-dental

The lower lip is the active articulator and the upper teeth are the passive articulator. English labio-dental sounds include [f] and [v].

dental

Dental sounds involve the upper teeth as the passive articulator. The active articulator may be either the tongue tip or (usually) the tongue blade -- diacritic symbols can be used if it matters which. Extreme lamino-dental sounds are often called interdental. English interdental sounds include [] and [].

alveolar

Alveolar sounds involve the alveolar ridge as the passive articulator. The active articulator may be either the tongue blade or (usually) the tongue tip -- diacritic symbols can be used if it matters which. English alveolar sounds include [t], [d], [n], [s], [z], [l].

postalveolar

Postalveolar sounds involve the area just behind the alveolar ridge as the passive articulator. The active articulator may be either the tongue tip or (usually) the tongue blade -- diacritic symbols can be used if it matters which. English postalveolars include [] and []. Linguists have traditionally used very inconsistent terminology in referring to the postalveolar POA. Some of the terms you may encounter for it include: palato-alveolar, alveo-palatal, alveolo-palatal, and even (especially among English-speakers) palatal. Many insist that palato-alveolar and alveo(lo)-palatal are two different things -- though they don't agree which is which. "Postalveolar", the official term used by the International Phonetic Association, is unambiguous, not to mention easier to spell.

retroflex

In retroflex sounds, the tongue tip is curled up and back. Retroflexes can be classed as apico-postalveolar, though not all apico-postalveolars need to be curled backward enough to count as retroflex. The closest sound to a retroflex that English has is []. For most North Americans, the tongue tip is curled back in [], though not as much as it is in languages that have true retroflexes. Many other North Americans use what is called a "bunched r" -- instead of curling their tongues back, they bunch the front up and push it forward to form an approximant behind the alveolar ridge.

palatal

The active articulator is the tongue body and the passive articulator is the hard palate. The English glide [j] is a palatal.

velar

The active articulator is the tongue body and the passive articulator is the soft palate. English velars include [k], [g], and [].

glottal

This isn't strictly a place of articulation, but they had to put it in the chart somewhere. Glottal sounds are made in the larynx. For the glottal stop, the vocal cords close momentarily and cut off all airflow through the vocal tract. English uses the glottal stop in the interjection uh-uh (meaning 'no'). In [h], the vocal cords are open, but close enough together that air passing between them creates friction noise.

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Note:

[w] is often called a "labio-velar". This doesn't follow the POA naming convention -- it does not mean that the active articulator is the lower lip and you try to touch your soft palate with it! A [w] is made up of two different approximants: a bilabial approximant and a (dorso-)velar approximant pronounced simultaneously.